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Forests influence climate through both the biochemical and biophysical processes, and the impacts of the latter on local climate may be much larger than the former. However, the biophysical effects of afforestation in arid regions have received little attention compared with afforestation in the tropic, temperate and boreal zones. In this study, we combined in situ eddy covariance flux measurements from a neighboring pairs of forested and background desert sites with the decomposed temperature metric (DTM) method to characterize the impacts of arid forests on surface temperature (T

Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the environmental factors that are responsible for the variations in species composition and richness of alpine shrublands using numerical methods. In the present study, we investigated vegetation and associated environmental variables from 45 sample plots in the middle Qilian Mountains of the northwestern China to classify different community types and to elucidate the species-environment relationships. We also estimated the relative contributions of topography and site conditions to spatial distribution patterns of the shrub communities using the variation partitioning. The results showed that four shrub community types were identified and striking differences in floristic composition were found among them. Species composition greatly depended on elevation, slope, shrub cover, soil pH and organic carbon. The important determinants of species richness were soil bulk density and slope. No significant differences in species richness were detected among the community types. Topography and site conditions had almost equal effects on compositional variation. Nonetheless, a large amount of the variation in species composition remained unexplained.

In this study, we examined the year 2011 characteristics of energy flux partitioning and evapotranspiration of a sub-alpine spruce forest underlain by permafrost on the Qinghai-Tibet Plateau (QPT). Energy balance closure on a half-hourly basis was H+lambda E = 0.81 x (R-n - G - S) + 3.48 (Wm(-2)) (r(2) = 0.83, n = 14938), where H, lambda E, R-n, G and S are the sensible heat, latent heat, net radiation, soil heat and air-column heat storage fluxes, respectively. Maximum H was higher than maximum lambda E, and H dominated the energy budget at midday during the whole year, even in summer time. However, the rainfall events significantly affected energy flux partitioning and evapotranspiration. The mean value of evaporative fraction (Lambda=lambda E/(lambda E + H)) during the growth period on zero precipitation days and non-zero precipitation days was 0.40 and 0.61, respectively. The mean daily evapotranspiration of this sub-alpine forest during summer time was 2.56mmday(-1). The annual evapotranspiration and sublimation was 417 +/- 8mm year(-1), which was very similar to the annual precipitation of 428 mm. Sublimation accounted for 7.1% (30 +/- 2mm year(-1)) of annual evapotranspiration and sublimation, indicating that the sublimation is not negligible in the annual water balance in sub-alpine forests on the QPT. The low values of the Priestley-Taylor coefficient (alpha) and the very low value of the decoupling coefficient (Omega) during most of the growing season suggested low soil water content and conservative water loss in this sub-alpine forest. Copyright (C) 2013 John Wiley & Sons, Ltd.

The Ejina Oasis (EO), located in arid northwest China, is a typical arid area in the world. The ecosystem in the oasis has become worse since the 1990s. However, it began to improve after the Chinese government took the mandatory measure to redistribute the water in Heihe in 2000. To understand this change, the remote sensing images in 1990, 2000 and 2006 were selected, and exertion related Land Use/Cover Change (LUCC) model was employed. Results showed that: (1) non-vegetation cover was the main body of the vegetation cover in oasis, showing a trend of increase at the beginning and diminution later, while low, medium and high vegetation cover was the other way around; (2) the area of low, medium and high vegetation cover in 2006 was less than that in 1990; the status and trend index P t of oasis vegetation cover was 0.62 in 1990–2000, which means that the oasis ecosystem of Ejina was getting worse and was under an unbalanced status; P t was 0.27 in 2000–2006 indicating that the oasis ecosystem was restored obviously and the whole system tended to be balanced; (3) all of these changes should be attributed to the water resources redistribution in Heihe River, which played a leading role, as well as the measures and relevant policies taken by the local government, which promoted the rapid recovery of the medium and high vegetation.

The Heihe River Basin is a typical arid inland river basin for examining stress on groundwater resources in northwest China. The basin is composed of large volumes of unconsolidated Quaternary sediments of widely differing grain size, and during the past half century, rapid socio-economic development has created an increased demand for groundwater resources. Understanding the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management of groundwater resources in the Heihe River basin. To this end, a total of 30 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions and its quality for irrigation. Chemical analysis shows that water presents a large spatial variability of chemical facies (SO4 2−–HCO 3 − , SO4 2−–Cl−, and Cl−–SO4 2−) as groundwater flow from recharge area to discharge area. The ionic ratio indicates positive correlation between the flowing pairs of parameters: Cl− and Na+(r = 0.95), SO4 2− and Na+ (r = 0.84), HCO3 − and Mg2+(r = 0.86), and SO4 2− and Ca2+ (r = 0.91). Dissolution of minerals, such as halite, gypsum, dolomite, silicate, and Mirabilite (Na2SO4·10H2O) in the sediments results in the Cl−, SO4 2−, HCO3 −, Na+, Ca2+ and Mg2+ content in the groundwater. Other reactions, such as evaporation, ion exchange, and deposition also influence the water composition. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. The results show that most of the groundwater samples are suitable for irrigation uses barring a few locations in the dessert region in the northern sub-basin.

The Ejina Basin, located in arid northwest China, is one of the most arid areas in the world. In recent years, rapid development has created a greater demand for water which is increasingly fulfilled by groundwater abstraction. Detailed knowledge of geochemical evolution of groundwater and water quality can improve the understanding of a hydrochemical system, and promote sustainable development and effective management of groundwater resources. To this end, a hydrochemical survey was conducted in the Ejina Basin in order to identify the major hydrochemical characteristics. The results of chemical analysis indicate that groundwater in the area is brackish. The major ions, TDS, and hydrochemical types of different areas are highly variable and show an obvious zonation from the recharge area to the discharge area. Saturation index (SI), calculated according to the ionic ration plot, indicates that the gypsum-halite dissolution reactions take place under the condition of the rock weathering to some extent, and evaporation is the dominant factor to determine the major ionic composition in the study area.

Hydro-chemical characteristics of groundwater and their changes as affected by human activities were studied in the Ejin Sub-Basin of the Inner Mongolia Autonomous Region, China, to understand the groundwater evolution, to identify the predominant geochemical processes taking place along the horizontal groundwater flow path, and to characterize anthropogenic factors affecting the groundwater environment based on previous data. The concentrations of major ions and total dissolved solids (TDS) in the groundwater showed a great variation, with 62.5% of the samples being brackish (TDS≥1000 mg L^(-1)). The groundwater system showed a gradual hydro-chemical zonation composed of Na(superscript +)-HCO(superscript – subscript 3), Na(superscript +)-Mg(superscript 2+)-SO(superscript 2 subscript 4)-Cl(superscript -), and Na(superscript +)-Cl(superscript -). The relationships among the dissolved species allowed identification of the origin of solutes and the processes that generated the observed water compositions. The dissolution of halite, dolomite, and gypsum explained, in part, the presence of Na(superscript +), K(superscript +), Cl(superscript -), SO(superscript 2- subscript 4), and Ca(superscript 2+), but other processes, such as mixing, Na(superscript +) exchange for Ca(superscript 2+) and Mg(superscript 2+), and calcite precipitation also contributed to the composition of water. Human activity, in particular large-scale water resources development associated with dramatic population growth in the last 50 years, has led to tremendous changes in the groundwater regime, which reflected in surface water runoff change, decline of groundwater table and degeneration of surface water and groundwater quality. Solving these largely anthropogenic problems requires concerted, massive and long-term efforts.

In the present study, the heat pulse technique was applied to investigate the stem sap flow of Populus euphratica in a desert riparian forest in an extreme arid region from April to October 2003 and from May to October 2004. The experimental sites were in Qidaoqiao (101°10′ E, 41°59′ N) and Bayantaolai farm (101°14′ E, 42°01′ N) in Ejina county, in the low reaches of the Heihe River, China. The results indicated that the diurnal change in the velocity of sap flow showed minor fluctuations. At night, the rising of sap flow could be observed in the main tree species because of root pressure. During the growing season, the maximum average velocity was observed in July, followed by August, and the same velocity was observed in September and May; the minimum velocity was observed in October. The transpiration from June to August during the growing season accounted for approximately 70% of the annual total transpiration. The sap flow velocity of P. euphratica trees of different ages could be arranged in the order: 15 yr > 25 yr > 50 yr. Sap flow velocity was closely related to changes in micrometeorological factors, with average sap flow velocity showing a significant linear correlation with net radiation, air temperature and relative humidity.

The unbridled development and use of water resources in the Tarim River basin over the last 50 years have led to a serious degradation of soil (>12×103 km2 of land desertified between the 1960s and 1990s) and water quality (rise in maximum salinity was from 1.3 g l−1 in 1960, to 4.0 g l−1 in 1981–1984, and to 7.8 g l−1 in 1998). Approximately 300 km of the lower reaches of the river course dried up between the 1950s and 1970s, seriously altering the downstream hydrological processes (a 4–6 m drop in groundwater levels from the 1960s to the 1980s, and 0.2 m yr−1 thereafter) and ecosystems (67% and 50% decrease (1958–1978) in Populus euphratica forest acreage and biomass, respectively). Between the 1950s and 1990s, 3820 km2 of P. euphratica forest and 200 km2 of shrub- and grassland were lost in the lower reaches of the Tarim River. In this study, based on estimates of soil organic carbon in desertified lands, it has been found that in the last 30 years (1970–2000), approximately 112 Tg of organic carbon (28% originating in the 0–1.0 m soil profile) has been released into the atmosphere as a result of soil degradation in the Tarim River basin. Intensive anthropogenic disturbance has been one of the foremost factors leading to the deterioration of water resources in this region. The key to solving these problems is to enhance the scientific and technical level of monitoring, management, and restoration of water resources and associated water and soil components of local ecosystems.

The deterioration of global eco-environment is seriously threatening human development, this is particularly true for most arid and semiarid zones in the world due to dry climate, meagre water resource, fragile ecosystem and prominent contradiction between the environment and development. How can we conduct eco-environmental construction is a difficult problem confronting people in these regions. This paper, taking northwest China's dry land miniature - Ejina desert oasis at the terminus of the Heihe River as an example and starting with the region's eco-environmental evolution, elucidates the cause of arid eco-environmental deterioration - interacted result of natural and human factors, analyze the restorability of eco-environment, discusses the problems in the eco-environmental construction in arid regions, and revealed results have a common reference value to the study of environmental evolution and eco-environmental construction in arid regions under the combined actions of natural and human factors.

A total of 340 soil samples from 17 different types of sandy land regions in China were analyzed for soil organic carbon (SOC). Stepwise regression served to identify correlations between SOC and a number of climatic factors measured at the sampling sites: winter, summer, nighttime and daytime air temperatures (AT) and precipitation. In desertified lands SOC showed a direct correlation with precipitation, but no significant relationship with the mean air temperature. However, in northwest and northeast China decreases in SOC were linked to rises in day/night and seasonal temperatures, while in north China they were linked to a rise in mean temperature. Over the entire study period (1950–1990), precipitation in the region decreased by 25 mm decade −1 , while the mean air temperature increased by 0.14°, 0.28° and 0.15° decade −1 in the northwest, northeast and north central regions, respectively. Driven by rises in day/night and seasonal temperatures, long-term alterations to global ecosystem processes, particularly the carbon cycle, may significantly alter the number and diversity of plants in desertified ecosystems. Based on multiple regression analysis, over the past 40 years, about 20% of emissions from SOC in the northeast were attributable to air temperature; in the north central region 31 and 16% of emissions were attributable to precipitation and mean AT, respectively; while in the northwest 28, 18 and 32% of the emissions were attributable to mean AT, nighttime temperature, and decreasing precipitation, respectively. It is obvious that human activities are the main single causative factor in the release of SOC-derived greenhouse gases to the atmosphere from desertified areas. DOI: 10.1111/j.1600-0889.2006.00169.x

While the global rise in mean day/night and seasonal air temperatures ( ATE) of recent decades is well documented, its influence on levels of soil-sequestered organic carbon, and on emission rates of CO2 and other greenhouse gases emanating therefrom, is only beginning to garner serious attention. This has resulted in a limited but growing understanding, particularly in the context of the lands of the Chinese subcontinent, of the mechanisms underlying such emissions. Some 340 soil samples from 12 different sandy land regions in China were analyzed for soil organic carbon (SOC) content. Stepwise regression identified correlations between SOC and a number of climatic factors measured at the sampling sites: winter, summer, nighttime and daytime ATE, and precipitation. In desertified lands, net SOC losses showed a direct correlation with precipitation but no significant relationship with mean ATE. However, in northwest and northeast China, decreases in SOC were linked to rises in day/night and seasonal ATE, while in north central China they were linked to a rise in mean ATE. Between 1900 and 1998, mean ATE in the northwest, northeast, and north central regions rose by 0.14E, 0.28E, and 0.15E decade(-1), respectively. Meanwhile, precipitation dropped by 25 mm decade(-1) across these regions. In this study, day/night and seasonal ATE showed differing levels of significance with respect to their linear relationships with SOC content. Driven by rises in day/night and seasonal ATE, long-term alterations to global ecosystemic processes, particularly the carbon cycle, may quantitatively and qualitatively alter the flora of desertified ecosystems. Our study suggests that, over the last 40 years, anthropogenic factors, precipitation, and rises in ATE (particularly nighttime and winter) have contributed 47%, 26%, and 20%, respectively, of greenhouse gas emissions from SOC. It is apparent that for China's desertified lands, human activity is the primary causative factor in the release of SOC-derived greenhouse gases to the atmosphere, while geography and climatic extremes individually play a lesser role.